Introduction to Programming Bertrand Meyer Last revised 1 December - PowerPoint PPT Presentation

1 Introduction to Programming Bertrand Meyer Last revised 1 December 2003 I ntroduction to Programming – Lecture 15 Chair of Softw are Engineering

2 Lecture 15: A glimpse into the hardware I ntroduction to Programming – Lecture 15 Chair of Softw are Engineering

Topics for this lecture 3 � Components of a computer system � Coding data � The memory hierarchy � Computer instructions � Computers´ power � Moore‘s law I ntroduction to Programming – Lecture 15 Chair of Softw are Engineering

Components of a computer system 4 What is hardware? � computers and related devices � physical machinery on which programs run I ntroduction to Programming – Lecture 15 Chair of Softw are Engineering

Coding data 5 � Data stored in computers’ memory represent diverse information: � Employee records � Images, sounds � Text in human languages � Numerical values for scientific computation � ... � Data must be represented (coded) in a way that is easy to read, write by computers � Binary coding is simple and efficient enough I ntroduction to Programming – Lecture 15 Chair of Softw are Engineering

The binary system 6 � As the name says: a set of two values 0 and 1 � The bit is the atomic variable for storing data bit = binary digit (possible values 0 and 1) � Also denotes a physical device with two states � Electronic bits: two different voltages � Magnetic bits: magnetized and unmagnetized I ntroduction to Programming – Lecture 15 Chair of Softw are Engineering

Computer revolution 7 Why did the binary systems displace all its competitors? Because the electronic industry lets us: � Build, pack very many bit representations into very small areas � Write and read these bits very quickly � Build devices storing these bits very cheaply I ntroduction to Programming – Lecture 15 Chair of Softw are Engineering

Relevancy to programmers 8 Why should programmers care? � Source code in human readible languages � But in memory binary representation � Addressing also in binary To fully understand the software systems we build we must understand how the physical machine represents, stores and accesses the data I ntroduction to Programming – Lecture 15 Chair of Softw are Engineering

Binary basics 9 � b2 b1 b0 bit byte sequence of 8 bits dec. (octet) 0 0 0 0 0 0 1 1 � w ord sequence of 4 bytes 0 1 0 2 (32 bits) 0 1 1 3 1 0 0 4 with n bits 2 n different � 1 0 1 5 1 1 0 6 values can be represented 1 1 1 7 n − 1 ∑ � decimal value of an n bit { } i dec : = b 2 , b ∈ 0 , 1 i i representation i 0 = I ntroduction to Programming – Lecture 15 Chair of Softw are Engineering

Representations 10 The extended ASCII character set: � digits, special symbols (‘~ ‘,‘@‘,‘$‘), 26 lower case and 26 upper case letters, accented letters � represented on 8 bits (256 possible values) � Eiffel type CHARACTER Numeric information: � integers (19), rationals (3/ 2), reals ( π ) � Eiffel types: � INTEGER , 1 w ord , 2 32 possibilities � REAL , 1 w ord , 2 32 possibilities � DOUBLE , 2 w ords , 2 64 possibilities I ntroduction to Programming – Lecture 15 Chair of Softw are Engineering

Addresses 11 � Address: starting position at which a data element appears in memory my_number : INTEGER ... 00000000 A18B0003h A18B0002h 00000000 my_number : = 5 A18B0001h 00000000 A18B0000h 00000101 start address of my_number 00000000h addresses memory I ntroduction to Programming – Lecture 15 Chair of Softw are Engineering

Powers of two 12 2 n n Approxim ation Com m on by pow er of 1 0 nam e 0 1 1 2 2 4 3 8 4 1 6 5 3 2 6 6 4 7 1 2 8 8 2 5 6 9 5 1 2 1 0 3 ( thousand) 1 0 1 0 2 4 Kilo ( K) 1 6 6 5 5 3 6 1 0 6 ( m illion) 2 0 1 ,0 4 8 ,5 7 6 Mega ( M) 1 0 9 ( billion) 3 0 1 ,0 7 3 ,7 4 1 ,8 2 4 Giga ( G) 4 x1 0 9 3 2 4 ,2 9 4 ,9 6 7 ,2 9 6 1 0 1 2 4 0 Tera ( T) 1 0 1 5 5 0 Peta ( P) I ntroduction to Programming – Lecture 15 Chair of Softw are Engineering

More on memory 13 What is the memory? � Where we put and access data � The place where we create and find objects Relevant parameters of memories: � persistency (persistent or transient) � access time (from ns to ms ) � capacity (from several KB to several GB) � maximum bandwidth (from GB/ s to MB/ s) � cost/ Byte I ntroduction to Programming – Lecture 15 Chair of Softw are Engineering

Memory hierarchy 14 Capacity Access tim e Bandw idth < 1 KB faster Registers < 0 .5 ns sm aller 2 0 -1 0 0 GB/ s 1 6 MB Cache < 0 .5 -2 5 ns 5 -1 0 GB/ s < 8 GB Main memory < 6 0 -2 5 0 ns 1 -5 GB/ s > 1 0 0 GB < 5 -1 0 m s Disk ~ 1 0 0 MB/ s infinite Tape slow er sec-m in bigger < 0 .0 1 GB/ s I ntroduction to Programming – Lecture 15 Chair of Softw are Engineering

Persistence 15 Memories are of two kind: Transient data are created and manipulated by programs, powering off the memory loses the data � transient memories: registers, cache, main memory � faster, smaller capacity, higher production cost � Persistent data remains forever unless deleted, powering off the memory has no effect on the data � persistent memories: disk, tape � slower, higher capacity, low production cost I ntroduction to Programming – Lecture 15 Chair of Softw are Engineering

Transient memory 16 � Processor operations access and modify data in transient memory � Synonims for main memory: primary memory, RAM (Random Access Memory), core memory I ntroduction to Programming – Lecture 15 Chair of Softw are Engineering

Persistent memory (1) 17 Secondary m em ory � extension for the main memory � attached to a computer � disk device (HDD) a pile of magnetized disks, with several reading heads � rotation speed, capacity, average access time, latency Rem ovable m em ory � devices for data backup � connected to a computer only episodically � disk devices, USB memory sticks, ZIP drives I ntroduction to Programming – Lecture 15 Chair of Softw are Engineering

Persistent memory (2) 18 I ntroduction to Programming – Lecture 15 Chair of Softw are Engineering

Moore’s “Law” 19 � Approximate doubling of computer power, for comparable price, every eighteen months Speed of Intel processors Pentium IV: 1.3 GHz 1 GHz (1 Hertz = 1 clock cycle per second) Pentium: 133 MHz 100 MHz 80486: 50 MHz 80386: 33 MHz 10 MHz to 1 GHz: 26 years 1 MHz from 1 to 2 GHz: 8 months 8008: < 1 MHz 1970 1980 1990 2000 I ntroduction to Programming – Lecture 15 Chair of Softw are Engineering

20 End of lecture 15 I ntroduction to Programming – Lecture 15 Chair of Softw are Engineering